Effects Of Internal Waves Research Articles

Internal tidal waves in Tiburon Basin (Gulf of California, Mexico) modulate fish larvae aggregations

To analyze the effects of internal tidal waves on fish larvae, a cruise was conducted (September 2012) in Tiburon Basin (∼400 m depth) in the Midriff Archipelago of the Gulf of California, an area of strong internal wave activity during periods of stratification. The temperature and current fields were correlated with the semidiurnal tide. The internal tide reached heights of ∼15 m, although a high-frequency event (period < 1 h) displaced isotherms up to 25 m. The kinetic energy was relatively high (>60 J m−3) for most of the sampling period. An increase in species richness and in the abundance of fish larvae was related to periods of high kinetic energy. A cluster analysis showed the presence of two groups of fish larvae. One group was associated with periods of high kinetic energy (>60 J m−3), with high fish larvae abundance (435 org 1000 m−3) and the frequent occurrence of coastal-demersal species (i.e. Erotelis armiger and Lythripnus zebra). A second group was associated with low kinetic energy (<35 J m−3) and had low fish larvae abundance (22 org 1000 m−3) and the absence of many coastal-demersal species. Results suggest that periods of high kinetic energy associated with internal tidal waves may be favorable for larval fish accumulation and may modulate fish larval assemblages in the Midriff Archipelago Region.

Sensitivity and feedback of wind-farm induced gravity waves.

Flow blockage by large wind farms leads to an upward displacement of the boundary layer, which may excite atmospheric gravity waves in the free atmosphere aloft and on the interface between the boundary layer and the free atmosphere. In the current study, we assess the sensitivity of wind-farm gravity-wave excitation to important dimensionless groups and investigate the feedback of gravity-wave induced pressure fields on wind-farm energy extraction. The sensitivity analysis is performed using a fast boundary-layer model that is developed to this end. It is based on a three-layer representation of the atmosphere in an idealised barotropic environment, and is coupled with an analytical wake model to account for turbine wake interactions. We first validate the model in 2D-mode with data from previous large-eddy simulations of "infinitely" wide wind farms, and then use the model to investigate the sensitivity of wind-farm induced gravity waves to atmospheric state and wind-farm configuration. We find that the inversion layer induces flow physics similar to shallow-water flow and that the corresponding Froude number plays a crucial role. Gravity-wave excitation is maximal at a critical Froude number equal to one, but the feedback on energy extraction is highest when the Froude number is slightly below one due to a trade-off between amplitude and upstream impact of gravity waves. The effect of surface friction and internal gravity waves is to reduce the flow perturbation and the related power loss by dissipating or dispersing perturbation energy. With respect to the wind-farm configuration, we find that gravity-wave induced power loss increases with wind-farm size and turbine height. Moreover, we find that gravity-wave effects are small for very wide or very long wind farms and attain a maximum at a width-to-depth ratio of around 3/2.

Modeling of three-dimensional sound propagation through solitary internal waves

An accurate and numerically efficient numerical model is very important for studying the effect of internal wave on underwawter sound propagation. A full-wave, three-dimensional (3D) coupled-mode model is able to deal with the internal wave problem with satisfactory accuracy, but such a model is in general numerically inefficient. A numerically efficient 3D model is presented for sound propagation in a range-dependent waveguide in the presence of solitary internal waves in this work. The present model is a forward-marching model that neglects backscattering. In this 3D model, an efficient two-dimensional (2D) coupled-mode model, C-SNAP, is adopted to compute 2D acoustic field solutions excited by a line source. The C-SNAP is a 2D forward-marching model, which uses an energy-conserving matching condition to preserve accuracy. An appealing aspect of C-SNAP is that its efficiency is competitive with that of the existing parabolic equation model. The integral transform technique is used to extend C-SNAP to a 3D model, where a complex integration contour is used for evaluating the wavenumber integral. A brief review of C-SNAP and formulation of the present 3D model are given. The forward-marching models are primarily suitable for treating the range-dependent problems with weak backscattering, such as with a slowly varying bathymetry. Since in general the backscattering from internal wave is weak, which is also validated numerically in this work, the present model is able to address the problem of sound propagation through internal wave with satisfactory accuracy. At the same time, it achieves an efficiency gain of at least an order of magnitude over that of full two-way, 3D model. In addition to the internal wave, the present model is also suitable for solving the general range-dependent problems where backscattering is weak, such as in the presence of a bottom ridge of a small height. Numerical simulations are also provided to validate the present model, where a two-way, 3D model serves as the benchmark. The numerical results show that the effect of the internal wave on the acoustic field is negligible for the region between the source and the internal wave. However, the effect is significant on the other side of the internal wave. A more interesting observation is the angular dependence of the interference pattern induced by the internal wave.

Wave formation in impact welding: Study of the Cu–Ti system

The cause of wavy interface morphology during impact welding is debated in the literature. In this paper, the effect of internal stress waves is investigated by varying the target (Cu 110) thickness during vaporizing foil actuator welding with constant thickness CP-Ti flyers. Experiments and smooth particle hydrodynamics simulations show that increasing target thickness causes the interfacial wavelength to increase, until it reaches about two times the flyer thickness. Also, to demonstrate the effects of consistency and transients of interfacial parameters, i.e., flyer velocity and wavy interface morphology, multi-probe photon Doppler velocimetry, electron microscopy and X-ray computed micro-tomography results are presented.

Incoherent source localization in random acoustic waveguides

ABSTRACTWe consider the problem of localizing one or more sources in a two-dimensional waveguide with horizontal flat boundaries and random sound speed fluctuations. Our data are the acoustic pressure field, measured on a vertical array of hydrophones that may span the entire depth of the waveguide or a part of it. We use randomness to model the effect of internal waves on the sound channel. Although the strength of the fluctuations is small, the transmitted signal is significantly affected from the multiple scattering of the waves with the random inhomogeneities, especially since we consider large propagation distances between the sources and the receiver array. Source localization is performed following an incoherent approach relying on a transport system of equations that describes wave propagation in random waveguides and that takes into account modal dispersion and energy transfer between modes.

Sound propagation effects of near-seabed internal waves in shallow water

Computational modeling is used to examine effects of near-seabed nonlinear internal waves. Waves of this type have been observed many times on the South New-England Shelf and elsewhere. The waves appear to be common when the dominant vertical density gradient zone is near the seabed. Many observations have been with profilers that alias the waves, or with instruments fixed to the seafloor that provide snapshots of passing waves. We have recently observed these features in greater detail using acoustic remote sensing from a ship, and we are now in a position to model their effects on sound propagation. Results are presented for many frequencies and many source/receiver/wave geometries. An important question remains about along-crest coherence of the waves, which would govern ducting and other anisotropic propagation effects. These waves are not as well studied as waves linked to a near-surface pycnocline, which can be studied remotely with EM via surface signature. The strong density gradients found in many shallow water areas allow the internal waves to have high frequencies, creating rapidly changing acoustics thereby shortening acoustic coherence time. The related strong sound-speed gradients, found both near the surface and near the seabed, are responsible for the important acoustic effects of the waves.

The Effect of Internal Gravity Waves on Fluctuations in Meteorological Parameters of the Atmospheric Boundary Layer

Variations in the intensity of turbulence during wave activity in the stable atmospheric boundary layer over a homogeneous steppe surface have been analyzed. Eight wave activity episodes recorded with a Doppler sodar in August 2015 at the Tsimlyansk Scientific Station of the Obukhov Institute of Atmospheric Physics have been studied. These episodes include seven trains of Kelvin–Helmholtz waves and one train of buoyancy waves. Variations in the rms deviation of the vertical wind-velocity component, the temperature structure parameter, and vertical heat and momentum fluxes have been estimated for each episode of wave activity. It has been found that Kelvin–Helmholtz waves slightly affect the intensity of turbulence, while buoyancy waves cause the temperature structure parameter and the vertical fluxes to increase by more than an order of magnitude.

An Investigation of the Effects of Internal Waves on Sound Propagation in a Stratified Medium with a Sloping Bed

Internal waves usually cause temporal and spatial changes of density and consequently affect the acoustic wave propagation in the ocean. The purpose of this study is a laboratory investigation of the effects of internal waves generated by oscillation of a cylinder in a large stratified glass tank with a sloping bed on the sound waves propagation. Results showed that sound waves are affected by internal waves that depend on the slope angle to the direction of internal wave propagation angle ratio. When the ratio is subcritical or supercritical, the acoustic signal is much reduced as compared to the case with no sloped bottom. This can be explained in terms of the internal waves energy reaching the sloped bed and their reflections.

Simulation of Internal Gravity Wave Propagation Due to Sudden Stratospheric Warming

The results of modeling the effect of stratospheric internal gravity waves (IGWs) excited in the region of sudden stratospheric warming (SSP) on the state of the upper atmosphere are presented. The numerical experiment used a two-dimensional model of atmospheric wave propagation including the dissipative and nonlinear processes accompanying the wave propagation. As a perturbation source, perturbations of temperature and density in a localized region at stratospheric altitudes during the SSW were considered. The amplitude and frequency of the perturbation source were evaluated from the results of observations and IGW theory. The results of numerical calculations showed that the heat source localized in the stratosphere excites IGWs with periods of up to several hours, which reach the thermospheric altitudes within a few hours. The maximum relative perturbations created by these waves relative to the unperturbed conditions were noted at altitudes of 100–200 km and at distances of up to ~1000 km from the source center.

Low frequency ambient noise modeling in the North Pacific: Simulation versus experiment

Farrokhrooz et al. [J. Acoust. Soc. Am., 2017] measured the seasonal variations of ambient noise in the 40–50 Hz band using long vertical arrays deployed during SPICEX, a 2004–2005 experiment in the northeastern Pacific. This talk compares simulations of low frequency noise from distant sources with the SPICEX data. The dominant sources of distant noise in the 40–50 Hz band are ships and wind. Noise from surface shipping and wind sources is transferred into the deep sound channel by several mechanisms [Dashen and Munk, J. Acoust. Soc. Am. 1984] and propagates long distances. The simulations use shipping density maps from exactEarth, Ltd., and measured wind speeds from European Centre for Medium-Range Weather Forecasts (ECMWF). A parabolic equation model that includes internal wave effects is used to generate Monte Carlo trials for different realizations of the shipping and wind environment. Results indicate that the seasonal variations in the SPICEX data are dominated by distant wind sources, including storms and persistent high latitude winds during the winter season. This comparison of simulation and experiment supports Bannister’s conclusions [J. Acoust. Soc. Am., 1986] regarding the role of high latitude winds in generating low frequency ambient noise. [Work sponsored by ONR.]

The Fate and Impact of Internal Waves in Nearshore Ecosystems.

Internal waves are widespread features of global oceans that play critical roles in mixing and thermohaline circulation. Similarly to surface waves, internal waves can travel long distances, ultimately breaking along continental margins. These breaking waves can transport deep ocean water and associated constituents (nutrients, larvae, and acidic low-oxygen waters) onto the shelf and locally enhance turbulence and mixing, with important effects on nearshore ecosystems. We are only beginning to understand the role internal waves play in shaping nearshore ecosystems. Here, I review the physics of internal waves in shallow waters and identify two commonalities among internal waves in the nearshore: exposure to deep offshore waters and enhanced turbulence and mixing. I relate these phenomena to important ecosystem processes ranging from extreme events to fertilization success to draw general conclusions about the influence of internal waves on ecosystems and the effects of internal waves in a changing climate.

Effect of nonlinear internal wave on monostatic reverberation in the shallow water region with underwater sound channel

The effect of nonlinear internal wave on reverberation is investigated for the shallow water region having an underwater sound channel, which was observed during SAVEX15 experiment. When source is located near the channel axis, the reverberation from rough bottom is insignificant because of trapped modes not interacting with the bottom. However, when a nonlinear internal wave is present, the reverberation level increases since trapped modes transfer to bottom interacting modes due to sound fluctuation by the nonlinear internal wave. This trend can be explained by the coupled mode equation [(2014). J. Acoust. Soc. Am. 135, 610-625]. To theoretically describe the increase of bottom reverberation, we simplify the situation where two modes are present; one is a trapped mode and the other is bottom interacting mode. In the situation, the trapped mode transfers to the bottom interacting mode after its encounter with the nonlinear internal wave. The bottom reverberation has different patterns and levels before and after the internal wave, and thus, it highly depends on the distance between source/receiver and internal wave.

Internal wave effects on seafloor imagery and bathymetry estimates

Large linear structures (tens of meters by several meters) have been observed recently in seafloor imagery and bathymetry collected with both synthetic aperture sonar (SAS) and multibeam echosounder (MBES) systems. It has been suggested [Hansen, et al., IEEE J. Oceanic Eng., 40, 621-631 (2015)] that this phenomenon is not due to the true morphology of the seafloor, but is caused by water column features related to breaking internal waves. Changes observed in acoustic intensity and bathymetry estimates are caused by a focusing of the acoustic field which results in structures that appear to be true seabed topography. In terms of seafloor mapping, these topography-mimicking features will impact the interpretation of imagery, may complicate the production of mosaics, and have the potential to cause bathymetric uncertainties exceeding International Hydrographic Organization standards. In this talk we will show that these water-column caused features may not be uncommon using examples of data collected with several different SAS and MBES systems in a variety of experimental locations.

Mode coherence in random matrix theory simulations

Random matrix theory (RMT) can be used to simulate the effect of internal waves on broadband acoustic mode time series in deep water, as described by Hegewisch and Tomsovic in several papers [Europhys. Lett. 2012; J. Acoust. Soc. Am. 2013]. Using RMT, narrowband mode propagation consists of the multiplication of a series of propagator matrices designed to model the mode coupling due to internal waves at a single frequency. In a recent paper, we varied the correlation of the mode coupling matrices with frequency and examined the effect on the time series generated via Fourier synthesis [Van Uffelen &amp; Wage, Inst. of Acoustics Conf., 2016]. This talk focuses on another key aspect of the RMT model, i.e., mode-to-mode coherence at a single frequency. Modes decorrelate as they propagate through internal waves. Building on Creamer's work, Colosi and Morozov use transport theory to analyze mode-to-mode coherence and mode energy in deep water environments [J. Acoust. Soc. Am., 2009]. This talk compares the energy and coherence results obtained with RMT methods to those from transport theory. [Work sponsored by ONR.]

Dongsha Atoll: A potential thermal refuge for reef-building corals in the South China Sea

Dongsha Atoll (also known as the Pratas Islands), the northernmost atoll in the South China Sea, experiences two contrasting physical phenomena: repetitive anomalies of the sea surface temperature exceeding the coral bleaching threshold and regular effects of the world's strongest internal waves resulting in the rhythmic upwelling of cold deep waters at the outer reef slopes of the atoll. This unique combination may result in significant differences in coral species composition and structure between the lagoon and forereef. Surveys conducted in August–September 2016 at 12 study sites in the 2–15 m depth range at Dongsha Atoll revealed a clear spatial separation between ‘thermally-susceptible’ stony coral genera, including Acropora, Pocillopora and Montipora, which mainly inhabited the forereef, and ‘thermally-resistant’ genera, including massive Porites, foliaceous Echinopora, Pavona and Turbinaria, which mainly resided in the lagoon. The mean coral cover and species richness on the forereef were respectively 1.8 and 1.4 times higher than those in the lagoon (61.3% and 98 species on the forereef vs. 34.2% and 69 species in the lagoon). Coral mortality rates, expressed as the ratio of dead to live stony corals, showed the same pattern (0.4 in the lagoon vs. 0.009 on the forereef). Furthermore, in a laboratory experiment, ‘thermally-susceptible’ taxa from the lagoon, (e.g. Pocillopora verrucosa and P. damicornis), exhibited higher resistance to bleaching than did their counterparts from the forereef. The present findings indicate that Dongsha Atoll is a potential thermal refuge for reef-building corals in the northern South China Sea and reveal the development of resilience and resistance to bleaching in coral communities of the lagoon.

Depositional and erosional bedforms in Late Pleistocene-Holocene pro-delta deposits of the Gulf of Patti (southern Tyrrhenian margin, Italy)

Multibeam bathymetry, high-resolution seismic profiles and seafloor samples have been analyzed to characterize depositional and erosional dynamics recorded pro-deltaic deposits and outer shelf sediments along of a sector of the NE Sicilian margin (southern Tyrrhenian Sea). The deltaic deposits cover an area of ca. 15km2 in front of the Mazzarrà River, and are morphologically characterized by waveforms trending overall along strike and incised cross-strike gullies of variable length. The gullies are shallow and characterized by small, coaxial erosive scours in the inner-middle shelf, whereas they become larger and deeper in the outer shelf-upper slope, in relation to the marked increase of slope gradients at the shelf break. Here, the wider gullies are characterized by a frame of crescent-shaped bedforms interpreted as cyclic steps, indicating the occurrence of sedimentary gravity flows in supercritical regime. Prodelta waveforms are widespread between −50 and −120m, with wave lengths of 34–110m and wave heights of 0.5–3m. Morphometric characterization and spatial distribution of the waveforms suggests a main role in their genesis played by hyperpycnal flows, although we cannot discard the possible effect of internal waves or slow deformation processes (i.e., creep).Depositional and erosional features similar to those observed on the seafloor are evident in the subsurface stratigraphy, revealing the onset and growth of the Mazzarrà Delta since the Last Glacial Maximum. The post-glacial sea level rise caused lateral shifts of the Mazzarrà River mouth controlling migration of depositional lobes and intensity of seafloor incision and sediment reworking, ultimately resulting in the observed wavy bedforms extending from the inner shelf to the upper slope.

Stimulated Imbalance and the Enhancement of Eddy Kinetic Energy Dissipation by Internal Waves

AbstractThe effects of internal waves (IWs), externally forced by high-frequency wind, on energy pathways are studied in submesoscale-resolving numerical simulations of an idealized wind-driven channel flow. Two processes are examined: the direct extraction of mesoscale energy by externally forced IWs followed by an IW forward energy cascade to dissipation and stimulated imbalance, a mechanism through which externally forced IWs trigger a forward mesoscale to submesoscale energy cascade to dissipation. This study finds that the frequency and wavenumber spectral slopes are shallower in solutions with high-frequency forcing compared to solutions without and that the volume-averaged interior kinetic energy dissipation rate increases tenfold. The ratio between the enhanced dissipation rate and the added high-frequency wind work is 1.3, demonstrating the significance of the IW-mediated forward cascades. Temporal-scale analysis of energy exchanges among low- (mesoscale), intermediate- (submesoscale), and high-frequency (IW) bands shows a corresponding increase in kinetic energy Ek and available potential energy APE transfers from mesoscales to submesoscales (stimulated imbalance) and mesoscales to IWs (direct extraction). Two direct extraction routes are identified: a mesoscale to IW Ek transfer and a mesoscale to IW APE transfer followed by an IW APE to IW Ek conversion. Spatial-scale analysis of eddy–IW interaction in solutions with high-frequency forcing shows an equivalent increase in forward Ek and APE transfers inside both anticyclones and cyclones.

RETRACTED: The Effects of Internal Waves on Propagation Behavior of Sound in the Sea

Short Retraction Notice The paper is withdrawn from Open Journal of Marine Science due to personal reasons from the corresponding author of this paper. This article has been retracted to straighten the academic record. In making this decision the Editorial Board follows COPE's Retraction Guidelines. The aim is to promote the circulation of scientific research by offering an ideal research publication platform with due consideration of internationally accepted standards on publication ethics. The Editorial Board would like to extend its sincere apologies for any inconvenience this retraction may have caused. Editor guiding this retraction: Prof. David Alberto Salas-de-Leon (EiC of OJMS) The full retraction notice in PDF is preceding the original paper, which is marked RETRACTED.

Modeling of the effect of internal gravity waves on upper atmospheric conditions during sudden stratospheric warming

We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of development of a sudden stratospheric warming (SSW), on upper atmospheric conditions. In the numerical experiment, we use a two-dimensional model of propagation of atmospheric waves, taking into account dissipative and nonlinear processes accompanying wave propagation. As a source of disturbances we consider temperature and density disturbances in the stratosphere during SSWs. Amplitude and frequency characteristics of the source of disturbances are estimated from observations and IGW theory. Numerical calculations showed that waves generated at stratospheric heights during SSW can cause temperature changes in the upper atmosphere. Maximum relative disturbances, caused by such waves, with respect to quiet conditions are observed at 100–200 km. Disturbances of the upper atmosphere in turn have an effect on the dynamics of charged component in the ionosphere and can contribute to observable ionospheric effects of SSW.

Effect of internal waves on acoustic energy structure in the northern East China Sea

Relation between depth direction acoustic energy and sound speed fluctuation caused by internal wave activity observed during SAVEX15 experiment is investigated. In the SAVEX15 region (northern East China Sea with water depths around 100 m), underwater sound channel was observed during May 2015 along with extensive internal wave activities. When the source is near the sound channel axis, most of the acoustic energy is trapped in the channel. However, internal waves change the sound speed profile, which results in spreading the acoustic energy over depth. Measured data during the experiment is used to investigate the relation between acoustic energy structure and internal wave activity. Parameters reflecting their variabilities are defined. Two main parameters are standard deviation of the acoustic energy integrated over depth and the sound speed gradient at the channel axis, which reflects the internal wave activity. The correlation of two parameters is used to show the effect of internal waves on the changes of acoustic energy distribution.